Improved Proxy Re-Encryption With Delegatable Verifiability

Abstract

Proxy re-encryption cryptosystem enables proxy to re-encrypt the ciphertext and protects the privacy of the corresponding plaintext. Hence, this type of cryptosystem has found tremendous applications in data sharing in cloud computing, email forwarding, securing file systems, and so on. In practice, proxy re-encryption has to support verification of ciphertext to reduce the users' computational burden. The ciphertext verification can be achieved through a public, private, or delegatable manner. Delegatable verification is more generic in that it can be easily converted into the other two verification methods. However, almost all existing schemes with delegatable verifiability only achieve replayable chosen ciphertext security. Hence, in this paper we propose a more secure proxy re-encryption scheme with delegatable verifiability. Specifically, we utilize a short signature scheme to prevent an attacker from forging a valid ciphertext, and prevent an attacker from forging a signature. As a result, our scheme is secure against chosen ciphertext attacks under the standard model.